Room temperature polymerizable silicone rubber compositions are described in U.S. Pat. Nos. 3,404,951 and 3,644,434 to Hittmair et al, in which compositions obtained by mixing a hydroxyl terminated linear organopolysiloxanes with amino-substituted organic silicon compounds are polymerized in the presence of atmospheric moisture.
Generally, these room temperature polymerizable compositions are exposed to atmospheric moisture for from about 5 to 30 minutes before the surface is tack-free.
Although some amino-substituted organosilicon compounds promote faster polymerization, the "pot-life" or "open-time" of the composition is not sufficient to provide adequate time for application. Consequently, slower polymerizing compositions are generally employed, which require a longer period of time for the surface to become "tack-free".
In many applications it is desirable to have a room temperature polymerizable composition which has a long "pot-life", but may be rapidly polymerized after it has been applied to a substrate.
One method for accelerating the polymerization of various organopolysiloxane compositions is to expose the compositions to a radiation source. Organopolysiloxane compositions which have been polymerized by a radiation source are described in U.S. Pat. No. 3,816,282 to Viventi, in which a composition consisting of a vinyl containing diorganopolysiloxane, a mercaptoalkyl substituted organopolysiloxane and a photosensitizer is exposed to a source of radiation.
Also, U.S. Pat. No. 4,362,674 to DuPont et al describes a process for making radiation cured articles which comprises treating an article molded into a desired shape from a composition containing hydroxyl-terminated organopolysiloxanes and a finely divided silica filler with an agent selected from ammonia gas, vapors of a volatile amine or a solution of a volatile amine to provide a transient cure in order to enable the molded article to withstand the stresses involved in mechanical handling during irradiation.
Although radiation polymerization of room temperature polymerizable compositions is not new per se, it has been found that radiation polymerization of room temperature polymerizable compositions free of a photo-initiator have certain advantages. For example, there are no residual fragments of photo-initiator present in the polymerized composition which will cause degradation of the polymerized composition. Moreover, the presence of photo-initiator will sometimes discolor the polymerized composition. Also, some photo-initiators are only slightly soluble in organopolysiloxane fluids and often bleed to the surface of the organopolysiloxane compositions.
In certain applications such as in assembly lines, the compositions must have a long "pot-life", but once it has been applied, rapid polymerization is necessary. It has been found that this may be achieved by exposing the compositions of this invention to an atmosphere of carbon dioxide during irradiation, even in the absence of photo-initiators. Of course, photoinitiators may be incorporated in the compositions of this invention to further accelerate the polymerization rate.
Therefore, it is an object of the present invention to provide radiation polymerizable organopolysiloxane compositions. Another object of the present invention is to provide organopolysiloxane compositions which are radiation polymerizable at ambient temperature. Still another object of the present invention is to provide organopolysiloxane compositions which are free of photo-initiators, but polymerize rapidly to a solid when exposed to a radiation source. Still another object of the present invention is to provide organopolysiloxane compositions having a long "pot-life", but when exposed to a radiation source, rapidly polymerize to a solid at ambient temperature. A further object of the present invention is to provide a process for polymerizing organopolysiloxane compositions which are free of photo-initiators. A still further object of the present invention is to provide organopolysiloxane compositions containing photo-initiators. A still further object of the present invention is to provide a process for accelerating the polymerization rate of organopolysiloxane compositions by exposing the organopolysiloxane compositions to a radiation source in the presence of carbon dioxide.